Stuart Mead is the CEO of Touch Bionics, a Scotland-based developer of upper-limb prosthetics. Touch Bionics recently presented the i-LIMB Hand, the first myoelectric device with five individually powered digits.

1.  How does the i-LIMB Hand advance myoelectrics?

The first [difference] is that the motor for each of the digits is individually powered. Each finger independently articulates, so we have five individually powered fingers which can shape to the thing that they’re gripping—and that’s different from anything that’s available today. That gives you a very natural and efficient grip.

The second thing is the thumb is rotatable to 90 degrees, much the same way our own thumb is. Whereas previous myoelectric hands could only be opened and closed, we have numerous different grip patterns. For example, patients are now able to point the index finger to operate a PC keyboard, or to rotate the thumb to meet the side of the index finger to hold a plate or turn a key in a lock. None of these functions have been possible before.

It also looks natural and moves like a real hand. [Its appeal is] the functionality, but it’s also an emotional thing about the hand looking more like a human hand.

2. Why is this hand able to move individual fingers where others weren’t?

We managed to find a way to put a motor inside each finger. There are five motors in the hand; other myolectric hands only have one motor. There’s a hollow piece of plastic in the position of the first phalange bone [of each finger], and the motor is inside that.

The fingers are collectively triggered by a traditional myoelectric signal generated by the patient—each finger closes down around an object, then stalls when it reaches a defined level of resistance. The result is a firmer, compliant grip that deals very well with odd-shaped objects such as a wine glass.

3. What qualities do patients need to use the hand well?

Well, the beautiful thing about our hand is that it utilizes the same electrodes and control inputs that other myoelectric devices use, but to control it, you use five motors instead of one. If [a patient] can use another myoelectric device, then he can use ours. The power that’s generated from the electrical signal is the same. In some ways, it’s easier because the hand is more adaptable.

4. What obstacles did you encounter in development of the hand?

We had an enormous number of challenges, but one [was] how to fit five motors into one shell the size of the human hand. All the power for the human hand comes from the muscles in the forearm. What we had to do was find a way to put the power inside the hand.

It has to be in many ways stronger than the human hand, because there’s no feedback from pain or sensory [input]—situations where the hand would be hurt, say. To provide a grip surface and to protect the hand from dust and water, we developed the i-LIMB Skin. This is a thin layer of semi-transparent material that wraps to every contour of the hand.

Also, [a] challenge has been finding a high-definition cosmesis (the flexible skin covering) of superior quality. By applying in-house expertise and partnering with companies that specialize in cosmesis, we achieved major breakthroughs for patients who wish their device to blend anatomically with the rest of their body, and have a life-like covering.

5. What is the next advancement you’re working on?

[For] the hand, we have a new control system which will allow us to have more input. Suppose you only had two electrode inputs to the hand but wanted to have more than two; we want to advance the technology so they have more control over hand function and individual finger dexterity.

While the hands and the digits were the first products to be launched, we also have in development a wrist rotator, an electric elbow, an electric shoulder, and an electric mid-humeral rotator, which allows you to move your arm from side to side. We did show some of those briefly at ISPO in Vancouver. We have all the joints powered for the upper limb.

We still have some development work to do, so I’d say 2008 or 2009 would be the earliest you’d see those products, but you will see some components of them before then. 

Interview by Heather Benjamin